1. Field of the Invention
The present invention relates to a player for an information recording disk, more particularly, to a player for an information recording disk on which a high frequency FM signal carrying a composite video signal and a low frequency digital signal modulated to carry information have been recorded in a superimposed manner.
2. Description of Background Information
Among this type of information-recording disks, a so-called digital-audio recorded video disk is known wherein a low frequency digital signal which has been produced by digitizing an audio signal by, for example, the EFM (Eight to Fourteen Modulation) method to provide a pulse train signal, is superimposed and recorded on the FM modulated signals of a so-called composite video signal, including sync signals such as horizontal and vertical sync signals, and of an audio signal (see Japanese Patent Application Provisional Publication No. 59-171011.)
In a player which can play this digital-audio recorded video disk, although a video demodulation system and a digital audio demodulation system each have a master clock, a jitter appears in the video output unless information is reproduced in phase synchronization with the master clock of the video demodulation system. Conventionally, therefore the speed control (spindle servo) of a spindle motor that rotationally drives a video disk is executed in accordance with the phase difference between a sync signal in a composite video signal read out from the video disk and in turn demodulated and a reference sync signal, while, in the digital audio demodulation system, a clock is generated in phase synchronization with a reproduction EFM signal phase-locked to a master clock of the video demodulation system and is used as a master clock of the digital audio demodulation system.
According to the conventional apparatus, the master clock of the digital audio demodulation system follows that of the video demodulation system and the spindle servo system intervenes in this phase control loop, so that the eccentric component of a disk is superimposed as disturbance on the master clock of the digital audio demodulation system. This eccentric component has been a cause to deteriorate the tone quality of the digital audio system.